


Underfell Gaster Blaster AU mashup

by TopazShadowwolf



Category: Undertale (Video Game)
Genre: Gaster Blaster AU, It's a Underfell Gaster Blaster mashup, Not the two different AUs meeting each other. One world, Some fighting so there's some violence, Some monsters get dusted but no one you'd care about, They weren't good monsters, Underfell AU, so I didn't mark that warning, think that's it, violent scenes aren't that graphic either, with underfell bros turning into giant blaster beasts
Language: English
Status: Completed
Published: 2018-10-14
Updated: 2018-10-14
Packaged: 2019-08-01 20:42:58
Rating: Teen And Up Audiences
Warnings: Creator Chose Not To Use Archive Warnings
Chapters: 1
Words: 2,463
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/16291430
Author URL: https://archiveofourown.org/users/TopazShadowwolf/pseuds/TopazShadowwolf
Summary: I did this for my "Gaster Blastober" thing I'm doing again this year. Last week I posted art that you can findhereif you want to see. This week is this fic. Hope you enjoy it.





	Underfell Gaster Blaster AU mashup

Sans never before wished he had a tongue. That weird fleshy object always seemed disgusting and a pain to deal with. Where did it fit in a mouth amid sharp teeth without getting bitten? With fangs like his, if he bit his tongue (that is if he had one) it would definitely be a painful experience. But, at that moment, as the wounds on his transformed body ached, he longed for some way to relieve the pain. He had seen other monsters lick their wounds before, and it seemed like such a comforting act. **  
**

All he had was his fang-filled jaws, which would only scratch and irritate the damaged areas. Well, he should be grateful. Had Boss not insisted that they do their rounds in their full blaster form he would be dust for sure. While still physically weaker than his brother in this form, as a blaster beast Sans had far more defense and HP than he normally had. Thanks to daily blaster scouting and training in dodging, this runt lived another day.

Still, as nice as it is to survive, the cracked and chipped bones were definitely something he could do without. Part of him wanted to retreat to the door in the woods. The lady there was good at healing, and few know that or even went there. Not even Papyrus knows about her, and Sans promised not to tell. She took a liking to Sans, for some reason he couldn’t explain. She liked his jokes at least, or she was that starved for the company that she tolerated him returning daily. Even in this large, lumbering form, when she couldn’t understand his jokes, she just opens the doors and walks out to sit with him and knit. He would like that right now, resting with her healing him and just being near; but, he knew Boss wanted Sans to wait here, to meet up once it was all clear.

The older blaster didn’t like that his younger brother ran off to scout their turf for any more of those punks from Waterfall. Sans had no warning for that surprise attack, and they were ready to fight him in this form. What they weren’t prepared for was Papyrus being close enough to provide back up. Knowing that Sans hated that Papyrus was alone when there could be more monsters ready to fight a blaster. Unfortunately, there was no stopping Boss, once he had an idea in his head he ran with it until he succeeded or failed in a way that made him feel he succeeded. In a world like this, that kind of productiveness was rewarded more than Sans laziness. So, he had long since passed pack leadership over to his bro. That did come with some interesting changes in Papyrus.

The younger skeleton now liked being called “Boss” when they were working or in public, no matter the form. Papyrus had also gotten nippy and rough in behavior, but nothing harmful. Sans wasn’t sure, but he wondered if it was his brother’s way of encouraging Sans to be more aggressive as well. Unfortunately for Boss, Sans was too lazy for that and would tuck tail, whine, and surrender. Not that Sans never “fought” back with his bro. He just preferred teasing Boss and testing his patience until Sans got that deserved nip on the nose or more. While it seemed worse to a watcher, no harm was ever done to either, and it was more bonding that not. Ultimately, the two were brothers, they had each other’s back… No matter the teasing or bullying they kept each other and their territory safe.

The sound of crunching snow alerted Sans to the return of his brother. His brother sniffed Sans over and growled softly. The older brother knew the growl wasn’t meant for him as Papyrus anger was still directed towards the jerks who thought they could invade their land and attack Sans. The younger blaster threw his head back and let out a roar that caused Sans to flinch. Papyrus stomped around angrily, blowing off steam in the process. Shifting his head slightly, Sans watched his brother with mild amusement.

<what now, boss?> Sans asked his brother once he finally settled down.

Papyrus looked at Sans for a moment then huffed while raising his head to full height in pride. <I SHALL TAKE THIS UP WITH UNDYNE. SHE AND I HAVE AND A LONG UNDERSTANDING ALLIANCE. I HIGHLY DOUBT SHE WOULD HAVE ISSUED THIS ATTACK>

It took an effort to shift his paws back under himself, but Sans slowly stood, snow falling from his aching bones from where he had pressed wounds against the cold for pain relief. They hurt, but he felt he could travel with no trouble. Even though he had not been sleeping just now, it still helped his magic to start to heal as he rested. <yeah, ok, makes sense, boss. besides, undyne’s the type who’d be here and not be just sending underlings. she might be in trouble herself, y’know.>

Turning, Sans started to walk towards the tunnel that lead to Waterfall, but as he started his brother snapped at him. Papyrus left a shallow scratch is previously undamaged snout with a fang. Sans jumped back lowering his tail while growling at Papyrus. <the hell was that for, boss?!>

<AND JUST WHERE DO YOU THINK YOU’RE GOING?!> Papyrus growled.

That surprised Sans and he tilted his head, unsure what his brother wanted from him. Didn’t Papyrus just say they were going to meet with Undyne? <uh, to waterfall?>

<ABSOLUTELY NOT! YOU WILL REPORT TO OUR DEN AND REST!> It was a clear order from Papyrus, but Sans glared at his brother.

<and let you wander into possible trap alone?> Sans snorted, annoyed his brother was blocking him.

<ARE YOU DOUBTING ME?!> Papyrus stood taller as he tried to appear threatening. Normally this display of self-confidence would cause Sans to laugh, but right now all Sans felt was worried.

<naw, of course not, bro. i just don’t doubt them either.> Sans huffed.

The younger brother growled deeply, the sound echoing like distant thunder with an underlying rolling hiss. Sans understood there was no arguing past this point. With a sigh, Sans sat and lowered his head to let his brother know he won this fight. His younger brother relaxed while still holding a strong stance. <GO HOME, SANS, REST. I WILL NOT BE LONG.>

Sans watched as Papyrus trotted off towards Waterfall as he slowly stood and started in the direction of Snowdin. But… had Papyrus knowns his elder brother well enough. He would have known Sans was not going to let Papyrus wander off into enemy territory like that. Just because his brother won the growling match, that didn’t mean he really won at all. Sans didn’t risk his life every day raising his younger brother just to have him killed by some punks who found out ways to fight a full-blown blaster beast. Keeping a safe distance, Sans trailed his brother, keeping an eye on him as they made their way to Waterfall. It wasn’t easy, as blasters had such strong senses, and Undyne’s house was a fair distance into Waterfall. But this wasn’t the first time Sans had followed his brother without Papyrus knowing.

There was plenty of long grass, deep water, and rock formations to hid behind, making it easy for Sans to remain hidden from his brother. Papyrus, though, was marching along, with no fear. Luckily for him, so far, none who saw him dared to approach. They had seen the Snowdin guard enough to know he was friends or allies with Undyne and understood it was in their best interest to leave him alone.

Sans always liked this place. Had it not been so populated, he would have stayed here with Papyrus instead of venturing into Snowdin. As two small pups, trying to survive without adult protection, it was far too dangerous with all the monsters living here. Unlike Waterfall, Snowdin had fewer monsters, and the ones that did live there formed a bond with their neighbors instead of small gangs. The cold and snowstorms could be just as deadly as a powerful monster, if not more so. When the world around you seems to be plotting your demise, waging war with everyone around you who could be a useful resource later is generally unwise. This made Snowdin a powerful unit of monsters who knew and understood how to work with each other far better than any other community in the Underground.

Still, it is easy to marvel at the beauty of Waterfall. In the darkness, the glowing echo flowers and mushrooms were wonderful to admire. More than them, though, the ceiling above looked like what he heard the night sky of the surface looked like. Millions of tiny dots above his head, shining in a gorgeous display that he could sit and look at for hours.

Unlike usual, it wasn’t difficult to overcome his desire to just sit and stare at those mock stars. He was here for a reason that was far more important to him. Keeping a socket on his brother, he continued to trail him to the house in question. The red hair of the monster out front gave away that she was the predatory, fish monster they were looking for. Sans glanced around, and sniffed the air, he didn’t see any threats around. Perhaps he was worried for nothing and should slink back home before Papyrus noticed.

“Papyrus? What are you doing here?” The gruff voice of Undyne asked his brother who started to shift down to a partial blaster form so he could speak to her. Something still nagged at Sans that he should keep an eye on them. With a sigh, he gave in to his instincts and remained hidden nearby, watching.

Hearing a noise, Sans turned his skull to see a shadowy figure of a monster lurking not that far from him. The cat monster hadn’t noticed Sans, his focus solely on Papyrus and Undyne. Sans could feel the ill intent radiating off of him. A yell from somewhere else signaled an attack, and before Undyne or Papyrus could react magic was flying at them. Luckily, both were skilled enough to block and avoid most of the magical bullets flying at them. As monsters ran out of hiding at them, Sans decided to even the odds a little. The cat monster was about to spring into action when Sans struck them with a well-placed slash of his claws. He could see the shocked and pained look of the feline. The cat monster took a turn and attacked him, but Sans dodged his magical attacks with a wince as the previously gained wounds ached from the use of his bones and joints. Annoyed, Sans sought to end this as soon as possible. He finished off the cat monster was just an easy pounce.

Dusting other monsters never sat well with Sans, but he did what needed to be done, for his survival and the survival of Papyrus. Looking back at his brother, he could see Undyne and Papyrus were holding their own fairly well, but they were still outnumbered. They would surely win, but it could go faster if they didn’t have so many to fight. He lowered his head and opened his jaws, feeling magic gathered then burst forth in a beam. His attack struck three monsters who were standing next to each other, and with their high LOVE, they were nothing but dust by the time the light of his attack died down.

His location known, Sans leaped from his hiding spot and struck at a monster with his claws. They stumbled back, clutching the wound, the pain from KR causing them then drop to their knees and scream. A yell from behind Sans caught his attention and he saw two monsters charging at him. Swinging his tail, he sent them flying off to who knows where. What mattered was they weren’t attacking his brother anymore.

“SANS! WHAT ARE YOU DOING HERE?! I TOLD YOU TO REST!” Papyrus yelled and to that Sans whined an apology. “IF YOU WERE REALLY SORRY YOU WOULDN’T BE HERE!”

Well, his brother had a point.

“Sans, stand down, we got it from here!” Undyne yelled, looking just as annoyed as Papyrus to see his help. This caused the attacking gang remaining to reconsider their options. After all, the one who just dusted three monsters in one attack was being told to stop helping. Good thing too. Papyrus and Undyne could both easily dust the rest of them without breaking a sweat. And as spears and bones rained down on them, those that weren’t dusted ran like the cowards they were.

Once they were alone, Papyrus turned to Sans and put his hands on his hips “SANS, YOU WERE GIVEN AN ORDER TO STAY HOME, WHY ARE YOU HERE?”

“Hey, normally I’m all for yelling at your brother, but look, he’s and not being lazy when he even had a good reason to sit around. And he did great, DID YOU SEE HOW FAR HE SENT THOSE TWO FLYING?! I bet they’re in Hotland!” Undyne smiled big, showing off her teeth as she spoke. She walked closer and reached up, patting Sans on the nose, letting him know she approved of this. “But, if you are ever so careless with your life again, I will dust you myself, got it?”

Sans blinked at her change of tone and nodded. He then waited patiently for his brother and Undyne to discuss what they were going to do about these attacks. Strengthening the patrols of the Royal Guards was the solution that they came to, which Sans worried would possibly lead to more trouble down the line. But, hey, what did he know, he was just a sentry.

Side by side, the two blasters made their way back to Snowdin. The younger fussing over Sans the entire way. <WHAT IF YOU GOT HURT MORE?> <YOU DID WELL IN THE FIGHT BUT YOU COULD HAVE JUST KEPT A SOCKET ON SNOWDIN!> <WHAT IF THEY SPOTTED YOU FIRST?> All it really boiled down to was that Papyrus had been worried about his older brother, and Sans was touched by this.

Once back home, they shifted back down into their skeleton forms. Papyrus ordered Sans to take a nap on the sofa after shoving a plate of spaghetti in the older skeleton’s face. The “food” was barely edible, but Sans managed to keep it down before curling up on the sofa. His body was still sore and tired from all that happened, but knowing his brother and their territory was still safe, Sans was able to drift to sleep.


End file.
